Why is this session value wrong?

The code of a verification code from the Internet I want to print the session value in the Yzm1.php page to see why
Is the value of the session different from the picture? Each time the yzm1.php page is refreshed, the string that is printed is the same as the string on the picture before the page refreshes, i.e. the string that appears on the picture, such as the value of Echo $_session["AAA" after refreshing once. Why are they not the same? So how do I do the verification?

yzm1.php

yzm2.php

!--? phpif (!isset ($_session)) {session_start ();} function Random ($len) {$srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm"; Mt_srand (); $strs = ""; for ($i = 0; $i $len; $i + +) {$strs. = $srcstr [Mt_rand (0, 30)]; } return $strs;} Randomly generated string $str = random (4); The width of the captcha picture $width = 50; The height of the captcha picture $height = 25; Declare the picture format of the layer you want to create @ header ("Content-type:image/png"); Create a layer $im = Imagecreate ($width, $height); Background color $back = Imagecolorallocate ($im, 0xFF, 0xFF, 0xFF); Blur point Color $pix = Imagecolorallocate ($im, 187, 230, 247); Font Color $font = imagecolorallocate ($im, 41, 163, 238); The point Mt_srand () of the Blur function; for ($i = 0; $i $i + +) {Imagesetpixel ($im, Mt_rand (0, $width), Mt_rand (0, $height), $pix);} Output character imagestring ($im, 5, 7, 5, $STR, $font); Output Rectangle Imagerectangle ($im, 0, 0, $width-1, $height-1, $font); Output Image imagepng ($im); Imagedestroy ($im); Select Cookie//setcookie ("Verification", $str, Time () + 7200, "/"); Select session$_session["AAA"] = $STR;? -->

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The code of a verification code from the Internet I want to print the session value in the Yzm1.php page to see why
Is the value of the session different from the picture? Each time the yzm1.php page is refreshed, the string that is printed is the same as the string on the picture before the page refreshes, i.e. the string that appears on the picture, such as the value of Echo $_session["AAA" after refreshing once. Why are they not the same? So how do I do the verification?

yzm1.php

yzm2.php

!--? phpif (!isset ($_session)) {session_start ();} function Random ($len) {$srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm"; Mt_srand (); $strs = ""; for ($i = 0; $i $len; $i + +) {$strs. = $srcstr [Mt_rand (0, 30)]; } return $strs;} Randomly generated string $str = random (4); The width of the captcha picture $width = 50; The height of the captcha picture $height = 25; Declare the picture format of the layer you want to create @ header ("Content-type:image/png"); Create a layer $im = Imagecreate ($width, $height); Background color $back = Imagecolorallocate ($im, 0xFF, 0xFF, 0xFF); Blur point Color $pix = Imagecolorallocate ($im, 187, 230, 247); Font Color $font = imagecolorallocate ($im, 41, 163, 238); The point Mt_srand () of the Blur function; for ($i = 0; $i $i + +) {Imagesetpixel ($im, Mt_rand (0, $width), Mt_rand (0, $height), $pix);} Output character imagestring ($im, 5, 7, 5, $STR, $font); Output Rectangle Imagerectangle ($im, 0, 0, $width-1, $height-1, $font); Output Image imagepng ($im); Imagedestroy ($im); Select Cookie//setcookie ("Verification", $str, Time () + 7200, "/"); Select session$_session["AAA"] = $STR;? -->

Don't say logic, just say code
First of all

function random($len) {    $srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm";    mt_srand();    $strs = "";    for ($i = 0; $i < $len; $i++) {        $strs .= $srcstr[mt_rand(0, 30)];    }    

The value of $STR is that way, so it doesn't have to be the same as long as you use YZM2 to get the verification code.

$str = md5($str); //选择 cookie//SetCookie("verification", $str, time() + 7200, "/"); //选择 Session$_SESSION["str"] = $str;

This is the time to write the value in the session, write $STR before the $str MD5 once, so you see the value is not generated $STR

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